Comments:

And yet the older they get, the more glaring the weakness: they can be killed easy due to easy dex loss. Ancient reds, for example only have 8 dex... Manage to hit them with enough debuffs to cause them to fall unconscious from 0 Dex and then issue the killing blow on a helpless enemy.

I'd suggest you look to see how many of them give dex penalty vs how many deal dex damage, as well as how many offer saves.

The simple rule is that if you are close enough to be able to touch him for Touch of Graceless, Calcific Touch, Excrutiating Deformity, or Fleshworm Infestation the dm is pulling punches. Heck even polar ray requires you to be at least 300 ft. Not to mention factoring in saves and spell resistance. They all require sr rolls. Then they all allow a fort save except polar ray.

This doesn't even factor in the fact that they have casting and can modify their spontaneous lists individually.

About the only way to win this is to be a wizard since pathfinder's wizards got super buffed with mindblank changes, between that and blindsight/sense cancellation and invisibility the dragon doesn't really have much of a chance. (especially given the short range on blindsense for them)

TL;DR You'd be surprised how quickly I can poke holes in things when you try to act big headed. "oh dragons are ez"

I talked to my GM who previously mentioned this tactic and he showed me the exact rule his players tend to abuse when dealing with enemies who would normally be hard to take down but have an otherwise easy to damage stat... Called shots.

A number of called shot rules can deal Dex (and other types) damage if you hit a crit or deal a debilitating blow.

Granted, debilitating blows will be damn near impossible on a dragon unless you're a munchkin on some flavor or another, but that's another discussion.

The Called Shots are explicitly optional and very hard to land. As for Inbetweenbooks I was more referring to that a wizard taking on a dragon can go greater invisible with mindblank and just blast the crap out of him from outside range of blindsense.